It's all about mentality and only you can change that.
I'll throw some tips out your way if you can take the time to understand them.
1.) Understand your character and the opponent and how you will beat them. Knowing a champion is essential. Cooldown's, CC, playstyle, Gap closers, etc... Some matchups you just can't beat though like Kassadin vs Pantheon, 99% of the time Kassadin will get smashed.(If people care to know why)
Here's the thought process... If I am playing Pantheon, my Q does more dmg than his Q, for lower mana costs. We're both melee but because I am AD I will do more melee damage allowing me to own the lane with my Q's and auto's. I also have a stun where he doesn't and Kassadin's signature move is his ulti. I am mantheon though and he will not get to level 6.
If you're playing Kassadin though against an aggresive pantheon... Thought process... He's melee so basically when he comes and attacks me he'll be farther away from his tower than a ranged champ would allowing a better chance for a succesful gank. I would call for a gank get my Q(Silence) And my E(Slow) at level 2, try to stack it up a little bit so when the gank happens I should have 6 stacks(need players even if it's enemy to cast a spell 6x) before you can use your E so maybe get it to 2-4 stacks before a jungle gank. I would BAIT him to stun me/Q me then jungle will come in... I know that my slow will enable for more hits to be done to my opponent and my silence will prevent him from casting spells(Even flash)
Essentially if pantheon stun's you in the middle of the lane, and a jungle like maokai has red buff and ganks him. Even if he flashes away kassadin's E and Q + Maokai W/Q and auto attacks should kill him. If pantheon is overextended(like pushing to your tower) it's a 100% kill pretty much.
Hope I didn't confuse anyone and hoped it help!